A solid-state drive (SSD) is a data storage device that uses integrated circuit assemblies as memory units to store data persistently. SSD technology uses electronic interfaces compatible with traditional block input/output (I/O) hard disk drives (HDDs). SSDs do not employ any moving mechanical components, which distinguishes them from traditional HDDs which store data on rotating magnetic disks using movable read-write heads.
Currently, most SSDs use NAND-based flash memory, which is a form of non-volatile memory which retains data in the absence of power and which can be electrically erased and reprogrammed (as flash memory was developed from EEPROM). Further, hybrid drives combine features of both SSDs and HDDs in the same unit, typically containing a hard disk drive and an SSD cache to improve performance of frequently accessed data. Flash memory stores information in an array of memory cells made from floating-gate transistors.
Solid state drives (SSDs) based on flash (NAND) memory are designed to be tolerant to an interruption of power and not to lose any data when experiencing such a power interruption. SSD drives generally have a non-volatile cache where data is kept, such as DRAM, and this data must be saved to the NAND memory in the event of a power loss interruption (PLI) event. Typically, an SSD contains capacitors or some other storage device with a purposefully sustained charge which provide enough power to save data to the NAND when a PLI interrupt signal is received. Data saved in response to a PLI event typically includes dirty write cache data and LBA mapping table information (e.g., indirection tables), which may include journaling data.
However, PLI problems typically require significant diagnostic efforts, which require the developer/troubleshooter to have possession of the drive in order to run tools on the drive to troubleshoot what happened during the power off sequence. Given the severity of the failure, where typically a drive may not come “ready” at poweron due to a data coherency sanity check, thus resulting in complete data loss, this long diagnostic turnaround time is not considered acceptable to customers.